Sunday, November 13, 2016

Using a Dell D220P-01

In case you don't know what a Dell D220P-01 is - it's a power supply for the SFF version of Dell's Optiplex 740 series PC. The neat thing about it is that unlike a traditional ATX PSU, this one is 12V only, so you get 220W @ 12V (18A) maximum and the PSU should not complain too much.
Another neat thing about them is that the PCs are legitimately junk, so you can get them even for free.
Stolen from
The pinout is in the picture, "P5" has to be connected to ground in order for it to turn on. Unlike newer server PSUs, this one can be connected straight from the start.
If you're like me and don't feel like butchering the connector, you'll need a breakout board. The connector is mechanically (!not electrically!) compatible with an 8-pin EPS12V power connector (plug is Molex 39-01-2080, PCB socket is  Molex 39-28-1083, terminals are Molex 39-00-0168 and Molex 44476-1111).
The 8-pin PCIe power connector is different with the placement of the square and hexagonal holes and is not mechanically compatible...not like that will stop the 200 pound gorilla from trying to jam it in...
Needles to say that if you plug this (and turn it on) into an EPS12V connector of a working motherboard, you will turn it into a non-working one, as the voltage is inconveniently reversed and the power supply will turn on. Results may vary from nothing at all to a spectacular fire and mini explosions of the caps.
stolen from
If your junkbox doesn't contain a motherboard with an 8-pin EPS connector, fret not, there is an alternative!
24-pin ATX...cut on the red lines...
stolen from wikipedia

Yep, it's not a true hack unless it involves a hacksaw!
side note - on any newer-ish junk motherboard, I suggest cutting the connector out, as the inner power layers use thicker copper (for heatsinking) and carry away heat from the soldering, making it very difficult.

As said earlier, plugging this PSU here to the MB is also not a good idea, although it should not turn on (results may vary). If the PSU does turn on, it will be short-circuited, if it "wins" over the short (burns through), it will send 12V to a 5V line...

Here's my quick and (really) gritty breakout board.

Yes, it's fugly, yes, it could've been nicer...I was going for "fugly, but functional". The crapton of solder should make sure that it can actually carry the 18A the PSU can deliver.
I kept the +12V rail from being at the edge, as it lowers the chance of an accidental short. The brass washers are actually soldered to the board.

Saturday, November 5, 2016

Smaller & lighter

While Totally not a bomb Mk II was useful for testing, it was a little too bulky even for the 1:10 car, so it was time to go shopping again...


  • 1x Raspberry Pi Zero 1.3
  • 1x 0.5mm pitch to 1mm pitch 15pin FPC cable
  • 1x TL-WN722N
  • 1x male RSMA connector with pigtail
  • some Kapton tape
  • enough 0.5mm sheet aluminium to make a box
  • ?x M2 screws
  • 1x XL6009 adjustable step up down Converter (DSN6000AUD)
The procedure:

1) Liberate the TL-WN722N out of it's plastic casing
2) perform UglyHack™ No.1 by desoldering the USB connector and solder on wires instead. Solder the other end fo the data lines into the USB port of the Rpi and solder the power to the power USB port of the Pi. PP1 is +5V, PP6 is gnd, PP22 is D+ and PP23 is D-. Twist the data lines to avoid weird shit from happening.
Grade-A hacking here!
the Kapton tape really is necessary...
Make liberal use of Kapton tape, covering all the exposed pads to avoid short circuits later.
3) Perform UglyHack™ No.2 by desoldering the RSMA connector and soldering on the pigtail one.
Again, Kapton tape is a must, not only as an electrical insulator, but also strain relief.

4) add the DC-DC power module (forgot pics, sry)
5) make an aluminium enclosure like so:
The other half is just a rectangular "U" shape, some of the holes are actually threaded.
6) Jam everything in, making sure that nothing is touching where it shouldn't.
In my implementation, the Pi is held a few mm away from the wall with screws and nuts on flexible washers. Some day I'll probably add a thermal pad between the main IC and the box, it does get warm.
The metal shield of the WiFi dongle is in direct contact with the wall to aid cooling, as it gets fairly hot when running with EZ-wifibroadcast. The DC-DC module is not even warm to the touch, so it can just float in the middle.
7) connect camera, strain-relive the cable so it doesn't get damaged.
Bottom scale is mm, top is inches.
Definitely could be made even smaller!

8) attach to desired mode of transport
Totally not a bomb Mk III
Camera holder needs to be adjustable...
Antennas for WiFi and RC
A few notes:
  • The antenna arrangement here is not ideal, the WiFi and RC systems interfere with each other, they should probably at least be further apart... (or I should use 5 GHz WiFi).
  • EZ-wifibroadcast on default runs outside of allowed WiFi bands (shhh, don't tell anybody...) and I keep it that way, there really isn't anything critical or even important using this band and it keeps the mutual interference with other WiFi to a minimum.
  • There are 5 GHz modules that are known to work with wifibroadcast if you want to avoid interference in the 2.4 GHz band.
  • The XL6009 module should safely operate between 4V to 30V. Pushing the voltage to the limits is asking for it.
  • The XL6009 is superior to LM2577 in that it runs at 400kHz instead of 50kHz, meaning the inductors can be much smaller.
  • If you feel lucky or actually know how to design a better DC-DC module, you can run both the dongle and Rpi directly on 3.3V. Be however aware, that if you fuck up, you'll fry them both.
  • If I ever make this smaller, I'll use one of the fancier DC-DC controllers that run at 1MHz, so the inductors are even smaller and the ripple is easier to filter out.
  • I advise using EZ-wifibroadcast as it boots much faster.
  • Last but not least, keep in mind that the sytem draws slightly over 2.5W and most of this is dumped as heat between the Rpi and the WiFi dongle, you have to allow air to flow around the box, otherwise it might overheat.